How to calculate Sum of averages for different level of detail?

[Actiknow]

We have information in a table with Sales by Invoice ID which is mapped to a Location and Area. Like below:

Invoice ID, Invoice Date, Location, Area, Sales

We want to get a summary where we see Avg sales per Location which is filtered by dates. This is then summarized at Area level to see total Sales by Area (sum of avg Sales by location).